qcow2: Make qiov match request size until backing file EOF

If a qcow2 image has a shorter backing file and a read request to
unallocated clusters goes across EOF of the backing file, the backing
file sees a shortened request and the rest is filled with zeros.
However, the original too long qiov was used with the shortened request.

This patch makes the qiov size match the request size, avoiding a
potential buffer overflow in raw-posix.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

diff --git a/block/qcow2.c b/block/qcow2.c
index 67e55c9667be6dbeeda29cd10771217d34e1f3e2..b0faa6917baf816c6d78a0242e70f83cca6d8f31 100644 (file)
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1020,11 +1020,20 @@ static coroutine_fn int qcow2_co_readv(BlockDriverState *bs, int64_t sector_num,
                 n1 = qcow2_backing_read1(bs->backing_hd, &hd_qiov,
                     sector_num, cur_nr_sectors);
                 if (n1 > 0) {
+                    QEMUIOVector local_qiov;
+
+                    qemu_iovec_init(&local_qiov, hd_qiov.niov);
+                    qemu_iovec_concat(&local_qiov, &hd_qiov, 0,
+                                      n1 * BDRV_SECTOR_SIZE);
+
                     BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING_AIO);
                     qemu_co_mutex_unlock(&s->lock);
                     ret = bdrv_co_readv(bs->backing_hd, sector_num,
-                                        n1, &hd_qiov);
+                                        n1, &local_qiov);
                     qemu_co_mutex_lock(&s->lock);
+
+                    qemu_iovec_destroy(&local_qiov);
+
                     if (ret < 0) {
                         goto fail;
                     }